The resonating valence bond state and high temperature superconductivity

A fluctuation theory is developed for the RVB state of high temperature superconductors in the Anderson model of high temperature superconductivity. The energy spectrum of fermion pairs in the RVB state is calculated by summing up a selected class of planar diagrams over all orders of perturbation theory. It is explicitly shown that the fermion pairs of the RVB state are pre-existing Cooper pairs which by undergoing a Bose condensation can become super-conducting Copper pairs. A part of the phase diagram is constructed showing conditions under which the RVB state becomes unstable with respect to both superconducting and magnetically ordered states.     

Crystal structures of oxidized and reduced stellacyanin from horseradish roots

Umecyanin (UMC) is a type 1 copper-containing protein which originates from horseradish roots and belongs to the stellacyanin subclass of the phytocyanins, a ubiquitous family of plant cupredoxins. The crystal structures of Cu(II) and Cu(I) UMC have been determined at 1.9 and 1.8 A, respectively. The protein has an overall fold similar to those of other phytocyanins. At the active site the cupric ion is coordinated by the N(delta1) atoms of His44 and His90, the S(gamma) of Cys85, and the O(epsilon)(1) of Gln95 in a distorted tetrahedral geometry. Both His ligands are solvent exposed and are surrounded by nonpolar and polar side chains on the protein surface. Thus, UMC does not possess a distinct hydrophobic patch close to the active site in contrast to almost all other cupredoxins. UMC has a large surface acidic patch situated approximately 10-30 A from the active site. The structure of Cu(I) UMC is the first determined for a reduced phytocyanin and demonstrates that the coordination environment of the cuprous ion is more trigonal pyramidal. This subtle change in geometry is primarily due to the Cu-N(delta1)(His44) and Cu-O(epsilon1)(Gln95) bond lengths increasing from 2.0 and 2.3 A in Cu(II) UMC to 2.2 and 2.5 A, respectively, in the reduced form, as a consequence of slight rotations of the His44 and Gln95 side chains. The limited structural changes upon redox interconversion at the active site of this stellacyanin are analogous to those observed in a typical type 1 copper site with an axial Met ligand and along with its surface features suggest a role for UMC in interprotein electron transfer.     

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.     

Chiral Motifs in Highly Interpenetrated Metal–Organic Frameworks Formed from Achiral Tetrahedral Ligands**

Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane-shaped cages in a single network, making these crystals new entries in the collection of diamondoid-type metal–organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks’ degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10-, 16-, and 32-fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å.     

Directing aryl-I versus Aryl-Br bond activation by nickel via a ring walking process

Activation of a strong aryl-Br bond of a halogenated vinylarene by nickel(0) is demonstrated in the presence of aryl-I containing substrates. eta2-Coordination of Ni(PEt3)2 to the C=C moiety of halogenated vinylarenes is kinetically preferable and is followed by an intramolecular aryl-halide bond activation process. This "ring-walking" process is quantitative and proceeds under mild reaction conditions in solution. Mechanistic studies indicate that the metal insertion into the aryl-halide bond is not the rate-determining step. The reaction obeys first-order kinetics in the eta2-coordination complexes with almost identical activation parameters for Br and I derivatives. The ring-walking process is kinetically accessible as shown by density functional theory (DFT) calculations at the PBE0/SDB-cc-pVDZ//PBE0/SDD level of theory.     

Fluxional behavior of platinum(0) complexes: intra vs intermolecular reaction pathways

The fluxional behavior of two analogous platinum complexes has been studied in solution by NMR spectroscopy to elucidate the reaction mechanism and to determine the activation parameters. This includes variable temperature NMR spectroscopy, 2D (1)H- (1)H exchange spectroscopy, and spin saturation transfer measurements. A platinum moiety, Pt(PEt 3) 2, translocates between two carbon-carbon double bonds of two vinylpyridine moieties bridged by an arene (i.e., phenyl, anthracene) at elevated temperatures. Magnetization transfer NMR experiments in the presence of free ligands unambiguously revealed an intramolecular pathway for the "phenyl" system. An intermolecular pathway is proposed for the "anthracene" complex.     

Hard modeling of ion chromatography separations on hydroxide-selective stationary phase

In the present paper the development and testing of the computer software for the simulation of the on-column ion chromatography separation processes are presented. The computer algorithm based exclusively on the selectivity coefficients of the tested analytes has been upgraded to cope with the 2:1 and 1:1 ratios of the analyte-to-eluent ion charge. The analytical solution of the cubic equation, which is needed for calculation of chromatograms for doubly charged analytes in the presence of singly charged eluent, is presented. The developed modeling approach was tested on the data sets produced by the system composed of hydroxide-selective stationary phase in combination with on-line electrolytically generated OH(-)-based eluents. Retention behavior of the selected anions on the AS15 (DIONEX, USA) stationary phase was investigated. The study of the dependence of the peak widths on the number of theoretical column segments considered in the calculated chromatograms enabled us to choose the optimal number of column segments. The average error in the retention time of the calculated chromatograms for the data set used in the study, i.e. seven different ions at eight different eluent concentrations was found to be 1.4%. A good match with the experimental chromatograms allows us to use the information of the intermediate states of calculations to get a detailed insight into the time-dependent on-column analyte distribution.     

Molecular assembly of a 3D-ordered multilayer

Combining strong metal-ligand coordination and pi-pi interactions affords a 3D-ordered molecular-based multilayer. The organization of the assembly is apparent from the optical properties and X-ray reflectivity.